Method and apparatus for measuring seismic parameters of a seismic vibrator

ABSTRACT

Apparatus and techniques for measuring seismic parameters, such as ground force, of a seismic vibrator used for generating seismic signals through a geological formation are provided. The seismic vibrator has a base plate positionable adjacent a ground surface of the geological formation. A sensor pad may be provided with an optical cable positionable between the base plate of the seismic vibrator and the ground surface of the geological formation, a laser for passing a light through the optical cable, and a detector for detecting disturbances in the laser light whereby a ground force applied to the ground surface may be determined.

RELATED CASES

The present application claims priority from U.S. application Ser. No.61/521,544, filed on 9 Aug. 2011, which is incorporated herein byreference.

FIELD OF THE INVENTION

The present invention relates generally to techniques for investigatinggeological formations. More specifically, the present invention relatesto seismic vibrators and related techniques for determining parametersof seismic operations, such as a true ground force signal produced bythe seismic vibrator and transmitted into the ground.

BACKGROUND OF THE INVENTION

The exploration of oil and gas may involve the investigation ofgeological formations to locate subsurface reservoirs. Seismic surveysmay be performed to gather data and/or generate images of geologicalformations at locations of interest. To generate the seismic surveys, aseismic source, such as a seismic vibrator or other surface orsub-surface energy source, may be used to generate acoustic wavesthrough the geological formations. For example, a vibroseis system mayinclude a truck with a base plate that may be lowered to the ground anda reaction mass driven by a hydraulic system to generate the acousticwaves. A receiver may be provided to measure the acoustic waves as theyrebound from the geological formations. Examples of seismic vibratorsare described in U.S. Pat. Nos. 4,664,223 and 4,184,144. Themeasurements captured by the receiver may be analyzed to determinegeological parameters and/or to generate two and/or three dimensionaldepictions of geological formations. This information may be used, forexample, to analyze potential oil fields and/or to design well plans forproducing hydrocarbons or other resources from the geologicalformations.

During operation, seismic vibrators may generate significant amounts ofharmonic energy. Such harmonic energy may affect the signals generatedby the seismic vibrators, thereby affecting measurements. Techniqueshave been developed to measure the ground force generated by a seismicvibrator, as described, for example, in U.S. Pat. No. 4,664,223 and inShan et al, “Load Cell System Test Experience: Measuring the VibratorGround Force on Land Seismic Acquisition,” SEG Houston 2009 Int'lExposition and Annual Meeting. Ground force measurements may be analyzedto make use of harmonic energy and enhance, for example, bandwidth ofsignals of the seismic vibrator.

Despite the development of advanced techniques for measuring certainseismic parameters, such as ground force, there remains a need toprovide enhanced seismic measurement capabilities and/or advancedtechniques for further enhancing seismic operations. The presentinvention is directed to fulfilling these needs in the art.

SUMMARY OF THE INVENTION

In at least one aspect, the techniques herein relate to a sensor pad formeasuring seismic parameters of a seismic vibrator. The seismic vibratoris for generating seismic waves through a geological formation. Theseismic vibrator has a base plate positionable adjacent a ground surfaceof the geological formation. The sensor pad includes an optical cablepositionable between the base plate of the seismic vibrator and theground surface of the geological formation, a laser for passing a lightthrough the optical cable, and a detector for detecting disturbances inthe light whereby a ground force of the seismic vibrator may bedetermined.

The optical cable may be distributed over at least a portion of the baseplate. The optical cable may be positionable in at least one windingalong an engagement surface of the base plate. The sensor pad may alsohave a protective layer positionable about the optical cable. Theprotective layer may be neoprene molded about the optical cable, or amat, a pad wafer, and/or an adhesive. The sensor pad may also have asecuring agent. The securing agent may be a bonding agent and/or anadhesive. The optical cable may be a fiber optic cable, amicroelectromechanical optical cable, and/or a distributed opticalcable. The optical cable may also be a single mode fiber optic cableand/or a multi-mode fiber optic cable. The sensor pad may also have atleast one sensor. The seismic parameter may be a ground force, a stress,and/or a strain.

In another aspect, the techniques herein may relate to a seismic systemfor measuring seismic parameters. The system may include a seismicvibrator for generating seismic waves through a geological formation anda seismic pad. The seismic vibrator has a base plate positionableadjacent a ground surface of the geological formation. The sensor padincludes an optical cable positionable between the base plate of theseismic vibrator and the ground surface of the geological formation, alaser for passing a light through the optical cable, and a detector fordetecting disturbances in the light whereby a ground force of theseismic vibrator may be determined. The seismic pad may be positionablebetween the base plate of the seismic vibrator and the ground surface ofthe geological formation. The system may also have an investigationunit.

In yet another aspect, the invention may relate to a method formeasuring seismic parameters. The method may involve positioning aseismic pad on a base plate of a seismic vibrator (the seismic padcomprising an optical cable, a laser, and a detector), positioning theseismic pad of the base plate adjacent a ground surface of a geologicalformation, generating seismic waves through the geological formationwith the seismic vibrator, passing a light from the laser through theoptical cable, and determining a ground force of the seismic vibrator bydetecting disturbances in the light. The method may also involveproviding a protective layer about the optical cable and/or securing theoptical cable in position.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the above recited features and advantages of the invention canbe understood in detail, a more particular description of the invention,briefly summarized above, may be had by reference to the embodimentsthereof that are illustrated in the appended drawings. It is to benoted, however, that the appended drawings illustrate only typicalembodiments of this invention and are, therefore, not to be consideredlimiting of its scope. The figures are not necessarily to scale, andcertain features and certain views of the figures may be shownexaggerated in scale or in schematic in the interest of clarity andconciseness.

FIG. 1 shows a schematic view of a system for generating seismic signalsthrough a geological formation having a seismic vibrator with a sensorpad for measuring seismic parameters of the seismic vibrator.

FIG. 2 shows a schematic view of a sensor pad of the system of FIG. 1.

FIGS. 3A-3C show various schematic views of an alternate sensor pad atvarious stages of assembly.

FIG. 4 is a flow chart depicting a method of measuring seismicparameters of a seismic vibrator.

DETAILED DESCRIPTION OF THE INVENTION

The description that follows includes exemplary apparatuses, methods,techniques, and instruction sequences that embody techniques of theinventive subject matter. However, it is understood that the describedembodiments may be practiced without these specific details.

Techniques for generating signals through a geological formation with aseismic vibrator are provided. Such techniques involve measuringparameters, such as ground force, of the seismic vibrator. Suchparameters may be used to monitor operation of the seismic vibratorand/or to enhance operation of the seismic vibrator (e.g., reduceattenuation, boost signal, enhance image resolution, etc.)

FIG. 1 depicts a seismic system (or vibrator) 100 usable for generatingseismic surveys of a geological formation 102 at a field ofinvestigation. The seismic system 100 includes a platform 104 positionedon a ground surface 103 of the geological formation 102. The platform104 is depicted as a truck movably positionable at the geological fieldof investigation 102. The seismic system 100 also includes a load (orreaction mass) 106 positionable on a carrier 105 of the platform 104.The seismic system 100 has an actuator 108 (e.g., a hydraulic system)for selectively activating a piston 107 for vibrating the load 106 togenerate acoustic waves through the geological formation 102. The piston107 is selectively extendable to place a sensor pad assembly 110 at anend thereof in contact the ground surface 103. The seismic system 100may be a conventional seismic vibrator for generating acoustic waves112, such as those described U.S. Pat. No. 4,664,223, and provided withthe sensor pad assembly 110 for enhancing measurement capabilitiesthereof.

The sensor pad assembly 110 has a base plate 105 with a sensor pad 111for contact with the ground surface 103. As shown in FIG. 1, the baseplate 110 may be a conventional base plate with a thin, rectangular bodyconfigured to engage the ground surface 103 and generate acoustic wavesthrough geological formation 102 beneath the ground surface 103. Thesensor pad 111 may be positioned between the base plate 105 and theground surface 103 for measuring seismic parameters during operation ofthe seismic system 100 as will be described further below.

The sensor pad 111 is coupled to an investigation unit 109 for capturingand processing data from the seismic system 100. The investigation unit109 may be, for example, a computer for receiving, storing, analyzing,displaying, communicating and/or otherwise manipulating data. Variousconventional devices, such as a memory, display, etc., may also beprovided in the investigation unit 109. The investigation unit 109 mayalso be coupled to a receiver 114 for receiving signals generated fromthe geological formation 104 as the seismic system 100 generatesacoustic waves 112 therethrough as depicted.

FIG. 2 shows a schematic assembly view of the sensor pad assembly 110 ofFIG. 1. The sensor pad assembly 110 includes the base plate 105 and thesensor pad 111. The base plate 105 may be conventional base plate usedwith conventional seismic vibrators. The base plate 105 may be a thinsheet of metal having an engagement surface 222 positionable adjacentthe ground surface 103 as shown in FIG. 1.

Optionally, the base plate 105 may be provided with sensors 281 formeasuring various seismic parameters of the seismic system 100 and/orthe environment about the seismic system 100. The seismic parameters maybe ground force, stress, strain or other measurements. For example,existing load cells, accelerometers, or other hydraulic or opticalsensors may also be used to generate additional data. One or more suchsensors 281 may be used separately or integrally with the optical cable220 to provide data. The optical cable 220 may be placed on an array ofload cells or other sensors 281 to measure ground force. The sensors 281may provide, for example, measurements at controlled or discretelocations for use in combination with the continuous or integratedmeasurements of the optical cable 220.

The sensor pad 111 may be positioned along the engagement surface 222 ofthe base plate 105 for engagement with the ground surface 103. As shown,the sensor pad 111 includes an optical cable 220 positioned in aneoprene layer 219 for attachment to the base plate 105. The sensor pad210 may be positioned with the optical cable 220 within the neoprenelayer 219 for direct (or near direct) contact with the surface 103. Theoptical cable 220 may be integrated into the neoprene protective layer219 to prevent damage that may be caused by the vibrator and/or themetal base plate 105 engaging the ground surface 103.

The neoprene layer 219 may be a conventional neoprene, such as theneoprene used to protect road surfaces. The optical cable 220 may behave the neoprene layer 219 molded thereabout, for example, by placingthe optical cable 220 into a mold for application of the neoprene layer219 thereon. The optical cable 220 may be positioned into a mold in thedesired configuration with the neoprene layer 219 applied thereto toprovide a protective layer about the optical cable 220 and form thesensor pad 111.

The optical cable 220 may be distributed along the entire engagementsurface 222 in, for example, a winding arrangement as shown. The opticalcable 220 may be distributed about the engagement surface 222 forachieving the maximum measurement coverage thereacross.

The optical cable 220 may be flexible to provide for desiredarrangements of the optical cable 220 about the base plate 105. Adesired amount of optical cable 220 may be distributed about the baseplate 105. Depending on the size and arrangement selected, the opticalcable 220 may generate, for example, about 200 channels per sample atabout a 5 m interval, or about 1,000 or more channels/samples at about alm interval. The optical cable 220 may be sufficiently flexible forplacement and/or for providing measurements at a desired number oflocations along the base plate 105, such as continuously over the entireengagement surface 222.

Any optical cable capable of measuring seismic parameters, such asvibration and/or other disturbances as described herein, may beemployed, such as a fiber optic or MEMS (microelectromechanical) opticalcable. The optical cable 220 may be, for example, a single mode or dualmode fiber optic cable. One such usable optical cable 220 may be a sixstrand, single mode, indoor/outdoor fiber, such as a conventionaltelecommunications cable. A given fiber optic cable used on a sensor padmay be, for example, a series of fiber optic cables of about 290 m inlength, or a continuous length of fiber optic cable of about 1740 metersin length, for a sensor pad 220 having an engagement surface 222 ofabout 2 m by 1 m.

Referring to FIGS. 1 and 2, a laser 225 may be provided to emit a laserlight 227 through the optical cable 220. As the optical cable 220receives vibrations, the laser light 227 passing through the opticalcable 220 may be disturbed. The optical cable 220 may have disturbancesin the laser light 227 at numerous points along the optical sensor 220,and may send a signal detectable by a detector (or investigator) 229.The detector 229 may be a conventional device capable of receivingsignals, such as those indicating disturbances in the laser light 227,from the optical cable 220. The detector 229 may be coupled to theinvestigation unit 109.

The investigation unit 109 may be used to analyze the signals from theoptical cable 220. Various seismic parameters, such as vibration of thebase plate 105 or vertical seismic profiling (VSP), may be determinedfrom a change in strain of the optical cable 220, or optical straindistributed at various points along the optical cable 220. Thepositioning of the optical cable 220 along the base plate 105 may beused to provide a ‘true’ picture of ground force integrated over theengagement surface 222 of the base plate 105.

Conventional distributed acoustic sensor (DAS) techniques may be used tosample the optical cable 220, and connect to numerous channels (e.g.,from about several hundred to thousands depending on the length of theoptical cable 220 and pulse intervals employed). Each channel maygenerate data that may be used to determine ground force about thesensor pad 210. A weighted sum of the signals may be used to estimateground force signals. The detector 229 and/or investigation unit 109 mayalso be used with the optical cable 220 to expand seismic bandwidth fromabout zero to about 10,000 Hz.

FIGS. 3A-3C depict an alternate sensor pad 111′ usable with the seismicsystem 100 of FIG. 1. The sensor pad 111′ includes an optical cable 220secured into a desired position with a securing agent as shown in FIGS.3A and 3B, and provided with protective layers thereabout as shown inFIG. 3C. The sensor pad 111′ may be provided with various combinationsof securing agents and/or protective layers for coating, protecting,securing and/or cushioning the optical cable 220.

As shown in FIGS. 3A and 3B, the optical cable 220 may be secured in adesired configuration using various securing agents. In FIG. 3A, theoptical cable 220 is distributed onto a mat 218 from a spool 333 andsecured to the mat 218 with a bonding agent 330, such as epoxy, glue,and the like. The bonding agent 330 is distributed at discrete locationsabout the mat 218 to secure (or bond) the optical cable 220 in place.The bonding agent is depicted as being applied in strips at variouslocations about the optical cable 220, but may be in any configurationsufficient to maintain the optical cable 220 in position.

Other securing agents may also be applied to the optical cable 220. FIG.3B shows the optical cable 220 secured into position with an adhesive332, such as rubber cement. The adhesive 332 may be used as a securingagent to secure the optical cable 220 in position. The adhesive 332 mayalso be used to coat the optical cable 220 and act as a protective layerthereon. The adhesive 332 may be used alone or in combination with thebonding agent 330. One or more securing agents, such adhesive 332,bonding agent 330 and/or other devices may be employed to secure theoptical cable 220 in position. Such securing agents may also act as aprotective layer over at least a portion of the optical cable 220.

FIG. 3C shows an assembly view of the sensor pad 111′ with variousprotective layers usable therewith. The optical cable 220 is shown withthe bonding agent 330 of FIG. 3A and the adhesive 332, but may haveother features positioned thereabout, such as the neoprene layer 219 ofFIG. 2. As shown in FIG. 3, additional protective layers, such as padwafer 216, rubber mats 218 and/or other layers, may also be provided.The optical cable 220 with the various protective layers may be securedtogether using a securing agent, such as the bonding agent 330 and/oradhesive 332 to form alternate sensor pad 111′. The alternate sensor pad111′ may be bolted onto the base plate 105 as shown in FIG. 1.

In some cases, the optical cable 220 may be positioned in one or moreprotective layers during transport and/or assembly. In such cases, oneor more pad wafers (e.g., plywood) 216 and/or mats (e.g., 0.5″ (1.27 cm)rubber mat) 218 may be provided in the sensor pad 111′ for assemblyand/or transport. During transport, the protective layers may be boltedtogether about the sensor pad 111′ and/or to the base plate 105. Once inposition, one or more of the protective layers may be removed. In somecases, one or more of the protective layers and/or securing agents, suchas adhesive 332, may be molded with the optical cable 220 into theneoprene layer 219 for operation therewith.

Other techniques may be used to secure the optical cable 220 in adesired position and/or protect the optical cable 220. While a specificarrangement of securing agents and protective layers are depicted, oneor more such features may be positioned about the base plate 105 and theoptical cable 220 to provide support thereto.

FIG. 4 is a flow chart depicting a method 400 for measuring a seismicparameter, such as ground force, of a seismic vibrator. The method (400)may involve positioning (440) a seismic pad on a base plate of a seismicvibrator (the seismic pad comprising an optical cable, a laser, and adetector), positioning (442) the base plate with the seismic pad thereonadjacent a ground surface of a geological formation, generating (444)seismic waves through a geological formation with a seismic vibrator,passing (446) a light from the laser through the optical cable, anddetermining (448) a ground force of the seismic vibrator by detectingdisturbances in the light. The method may also involve providing aprotective layer about the optical cable and/or securing the opticalcable in position. The steps of the method may be performed in a desiredorder, and repeated as desired.

While the present disclosure describes specific aspects of theinvention, numerous modifications and variations will become apparent tothose skilled in the art after studying the disclosure, including use ofequivalent functional and/or structural substitutes for elementsdescribed herein. For example, aspects of the invention can also beimplemented in one or more sensor pads and/or one or more optical cablesof one or more seismic vibrators. All such similar variations apparentto those skilled in the art are deemed to be within the scope of theinvention as defined by the appended claims.

Plural instances may be provided for components, operations orstructures described herein as a single instance. In general, structuresand functionality presented as separate components in the exemplaryconfigurations may be implemented as a combined structure or component.Similarly, structures and functionality presented as a single componentmay be implemented as separate components. These and other variations,modifications, additions, and improvements may fall within the scope ofthe inventive subject matter.

1. A sensor pad for measuring seismic parameters of a seismic vibrator,the seismic vibrator for generating seismic waves through a geologicalformation, the seismic vibrator having a base plate positionableadjacent a ground surface of the geological formation, the sensor padcomprising: an optical cable positionable between the base plate of theseismic vibrator and the ground surface of the geological formation; alaser for passing a light through the optical cable; and a detector fordetecting disturbances in the light whereby a ground force of theseismic vibrator may be determined.
 2. The sensor pad of claim 1,wherein the optical cable is distributed over at least a portion of thebase plate.
 3. The sensor pad of claim 1, further comprising aprotective layer positionable about the optical cable.
 4. The sensor padof claim 3, wherein the protective layer is selected from the groupconsisting of neoprene molded about the optical cable, a mat, a padwafer, an adhesive layer, and combinations thereof.
 5. The sensor pad ofclaim 1, further comprising a securing agent between the cable and thebase plate.
 6. The sensor pad of claim 1, wherein the optical cable isone of a single mode fiber optic cable, a multi-mode fiber optic cable,a microelectromechanical optical cable, a distributed optical cable andcombinations thereof.
 7. The sensor pad of claim 1, further comprisingat least one sensor.
 8. The sensor pad of claim 1, wherein the seismicparameter is one of a ground force, a stress, a strain, and combinationsthereof.
 9. A method for measuring seismic parameters, comprising:positioning a seismic pad on a base plate of a seismic vibrator, theseismic pad comprising an optical cable, a laser, and a detector;positioning the seismic pad of the base plate adjacent a ground surfaceof a geological formation; generating seismic waves through thegeological formation with the seismic vibrator; passing a light from thelaser through the optical cable; and determining a ground force of theseismic vibrator by detecting disturbances in the light.
 10. The methodof claim 9, further comprising providing a protective layer about theoptical cable.